A known method of installing a resin grouted rock bolt to secure the roof or wall of an underground mine, tunnel or other ground excavation involves mounting a two component resin filled cartridge on the upper end of the rock bolt and inserting the assembled resin cartridge and rock bolt into a hole drilled into the rock face. When the resin cartridge reaches the top end of the hole, the upper end of the rock bolt pierces the resin cartridge, enabling the two resin components to be mixed. Mixing of the resin components is typically achieved by rotating the rock bolt within the hole. The mixed resin sets in the annular cavity between the upper end portion of the rock bolt and the wall of the hole in the rock face, thereby anchoring the upper end of the rock bolt.
The resin cartridge is typically mounted on the upper end of the rock bolt by way of a cardboard sleeve mounted concentrically on and extending beyond the upper end of the rock bolt. The resulting assembly of the rock bolt and externally mounted resin cartridge is, however, relatively long, having a length equal to the combined lengths of the rock bolt and the resin cartridge. As a result, such an assembly cannot be utilised in more confined areas such as mines or tunnels having a low roof height, as there is insufficient room to manoeuvre the assembly on a rock bolt installation rig and align it with the hole in which the assembly is to be inserted. Further, externally mounted resin cartridges are prone to damage during maneuvering of the rock bolt installation rig within the mine/tunnel and during installation of the rock bolt assembly itself.
Alternate rock bolts have been proposed that are of a tubular form, allowing a resin cartridge to be mounted within the hollow body of the rock bolt. A resin cartridge rupturing device is located in the hollow body above the resin cartridge. Formations on the inner wall of the hollow body between the rupturing device and the open upper end of the rock bolt form a static mixing device which serve to mix resin passing therethrough. The tubular rock bolt is inserted into the hole with a plunger extending from the lower end using a typical rock bolt installation rig. Once the rock bolt is placed in position, the plunger is forced through the rock bolt hollow body, forcing the resin cartridge against the rupturing device, thereby rupturing the cartridge and extruding the two component resin through the static mixing device formations on the interior wall of the rock bolt. Mixed resin then flows out of the end of the rock bolt and into the annular cavity between the rock bolt and the hole wall, where it sets so as to secure the end of the rock bolt. The static mixing device and cartridge rupturing device, are, however subject to blockage from fragments of the ruptured casing of the resin cartridge, thereby inhibiting the flow and adequate mixing of the two component resin. Further, given that the plunger typically needs to be mounted in the rock bolt prior to insertion with a standard rock bolt installation rig, the assembly of the rock bolt and plunger suffers from the same disadvantages of excess length discussed above in relation to rock bolt assemblies having externally mounted resin cartridges.